This invention relates to a window washer for a motor vehicle adapted to deposit a window washer fluid in a consistent position on a vehicle window regardless of washer fluid temperature. The vehicle window washer system is of the type in which the washer fluid is sprayed onto the window through a nozzle by a motor driven pump; and the spray or projection characteristics of the washer fluid are partially determined by the fluid's viscosity, which varies with ambient temperature. Since the washer fluid is projected by the nozzle through the air at the window and the fluid, while in the air, is affected by gravity, air currents and other environmental factors, the speed at which the individual droplets of washer fluid leave the nozzle partially determines the points at which they hit the window. The speed of the washer fluid droplets is determined by the fluid pressure at the nozzle and the viscosity of the fluid. With a substantially constant pump outlet pressure, there can be a significant difference in the deposit position or pattern on the window over the temperature range typical of motor vehicle operation.
The known prior art in the field of vehicle window washer and wiper systems does not deal directly with this problem. Kibler U.S. Pat. No. 3,286,932 discloses a "winter-summer" windshield washer system in which a valve is operable by the vehicle operator to select between two fluid supplies, one comprising a tank of washer liquid pumped by an electric motor for normal windshield cleaning and the other comprising a tank of alcohol/water pumped by compressed carbon dioxide for winter cleaning or removal of bugs, etc. However, this prior art does not discuss or propose apparatus which automatically corrects for temperature induced variations in the viscosity of the washer fluid. Another prior art publication, Keddle U.S. Pat. No. 3,591,887, shows a windshield washer with a pump fed through a selector valve to select hot or cold fluid for normal or defrosting applications; but this disclosure also does not show viscosity correction of the washer fluid. Temperature controls of washer fluid are also known, as in Merkle U.S. Pat. No. 3,243,119 and Rocchitelli U.S. Pat. No. 4,508,957; but these require additional fluid heating and piping apparatus.